Introduction to submerged arc furnace
Submerged arc furnace is also known as electric arc furnace or electric resistance furnace. It is mainly used for reducing and smelting ores, carbon reducing agents, solvents and other raw materials. It is mainly used to produce ferrosilicon, ferromanganese, ferrochrome, ferrotungsten, silicon manganese alloy and other ferroalloys, which is an important industrial raw material in the metallurgical industry. It is characterized by the use of carbon or magnesium refractory material as furnace lining and the use of self-growing electrodes. The electrode is inserted into the charge for submerged arc operation, and the energy and current of the arc pass through the charge, and the energy is generated by the resistance of the charge to melt the metal, and the charge is added successively, and the slag is discharged intermittently, and the industrial electric furnace is operated continuously.
Structural characteristics
Submerged arc furnace is a kind of industrial electric furnace which requires huge power consumption. It is mainly composed of furnace shell, furnace cover, furnace lining, secondary conductors and terminals, water cooling system, smoke exhaust system, dust removal system, electrode shell, electrode pressure release and lifting system, charging and discharging system, electrode holder, burn-through device, hydraulic system, submerged arc furnace transformer and various electrical equipment.
According to the structural characteristics and working characteristics of the submerged arc furnace, 70% of the system reactance of the furnace is generated by the secondary conductors and terminals. The secondary conductors and terminals are a high current working system, the maximum current can reach tens of thousands of amperes, so the performance of the secondary conductors and terminals determines the performance of the furnace, it is precisely because of this reason that the natural power factor of the furnace is difficult to reach more than 0.85. The natural power factor of the vast majority of the furnace is between 0.7 and 0.8, the lower power factor not only reduces the efficiency of the transformer, consumes a lot of useless work, and is charged additional electricity fines by the electricity department, but also due to the manual control of the electrode and the process of the pile, resulting in the increase of the power imbalance between the three phases, the highest imbalance can reach more than 20%. This leads to low smelting efficiency and higher electricity costs, so improving the power factor of the secondary conductors and terminals and reducing the imbalance of the power grid has become an effective means to reduce energy consumption and improve smelting efficiency. If appropriate measures are taken to improve the power factor of the secondary conductors and terminals, the following effects can be achieved:
(1) Reduce power consumption by 5 ~ 20%
(2) Increase the output by more than 5% to 10%.
Method and principle
Under normal circumstances, in order to solve the problem of low power factor of submerged arc furnace, China currently generally adopts capacitance compensation, usually reactive power compensation at the high voltage end, but because the high voltage end compensation can not solve the problem of three-phase balance, and because the inductance of the secondary conductors and terminals accounts for more than 70% of the entire system inductance, the high voltage end compensation did not achieve the reduction of the secondary conductors and terminals system inductance and improve the power factor of the secondary conductors and terminals.
Therefore, some companies have taken reactive power compensation measures at the same time of high and low voltage on the newly built furnace to solve the above problems. Compensation at the secondary conductors and terminals end can greatly improve the power factor at the secondary conductors and terminals end and reduce power consumption. In view of the large amount of reactive power consumption and imbalance of the secondary conductors and terminals at the low voltage side of the furnace, the reactive power compensation technology transformation is implemented while effectively improving the power factor. Technically speaking, it is reliable and mature, and economically speaking, input and output are proportional.
In the low-pressure side of the ore furnace, the reactive power compensation implemented for the three-phase imbalance caused by the inconsistency between the reactive power consumption and the layout length of the short-net has incomparable advantages in improving power factor, absorbing harmonics, and increasing production and reducing consumption.
However, due to the high cost and the poor working environment, the service life is greatly affected, and the reactive power compensation at the low voltage end of the secondary conductors and terminals also brings the increase of harmonics, so measures must be taken to suppress the 3 ~ 7 harmonics, which increases the investment, lengthens the investment recovery cycle, and at the same time, the follow-up maintenance costs are high and the comprehensive benefits are not good. Generally, this means is only applicable to new furnaces.
